Magnetic resonance imaging (MRI) has been used successfully to study blood flow in vivo. Moreover Villringer et al. Magnetic Resonance in Medicine 6:164-174 (1988), Cacheris et. al. Society of Magnetic Resonance in Medicine, 7th Annual Meeting, San Francisco, 1988, (SMRM 1988) Works in Progress, page 149, Belliveau et. al. SMRM 1988, Book of Abstracts, page 222 and Moseley et. al. SMRM 1988, Book of Abstracts, page 43 have proposed the use of certain paramagnetic lanthanide chelates as magnetic susceptibility, that is T.sub.2 * shortening, MRI contrast agents for studies of cerebral blood flow and perfusion.
Unlike many previous imaging procedures, T.sub.2 or T.sub.2 *-weighted MRI using magnetic susceptibility (MS) contrast agents (hereinafter MS imaging) enabled blood perfusion deficits, e.g. cerebral ischemias, to be visualized rapidly as the MR signal intensity was reduced in the regions of normal perfusion due to the effect of the contrast agent, with ischemic tissue being revealed by its retention of signal intensity.
Blood perfusion deficits are associated with several serious and often life-threatening conditions. Rapid identification and location of such deficits is highly desirable in order that the appropriate corrective action, be it therapeutic or surgical, may be taken promptly. Thus in the case of cerebral ischemia, any delay in post ischemic recirculation and reoxygenation of brain tissue reduces neuronal survivability.
MS imaging therefore represents a major improvement over routine T.sub.2 or T.sub.2 *-weighted imaging in the absence of MS contrast agents, since in the routine procedures ischemias or infarcts only become detectable 2 to 3 hours after the event, e.g. a stroke, which gave rise to the perfusion deficit. However, while determination of the existence and location of a perfusion deficit is important, it is also desirable to be able to detect the degree or severity, and if possible the onset and duration of blood flow abnormalities or variations, in a quantifiable manner. We now propose that this be done using a modified MS imaging procedure.